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Wed, 21 May 2025 18:50:34 +0000 From: Kuniyuki Iwashima To: CC: , , , , , , , Subject: Re: [Bug] "WARNING in should_fail_ex" in Linux kernel v6.14 Date: Wed, 21 May 2025 11:50:22 -0700 Message-ID: <20250521185026.56042-1-kuniyu@amazon.com> X-Mailer: git-send-email 2.49.0 In-Reply-To: References: Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit Content-Type: text/plain X-ClientProxiedBy: EX19D036UWC002.ant.amazon.com (10.13.139.242) To EX19D004ANA001.ant.amazon.com (10.37.240.138) From: John Date: Wed, 21 May 2025 22:13:15 +0800 > Dear Linux Kernel Maintainers, > > I hope this message finds you well. > > I am writing to report a potential vulnerability I encountered during > testing of the Linux Kernel version v6.14. > > Git Commit: 38fec10eb60d687e30c8c6b5420d86e8149f7557 (tag: v6.14) > > Bug Location: net/ipv4/ipmr.c:440 ipmr_free_table net/ipv4/ipmr.c:440 > > Bug report: https://pastebin.com/xkfF5DBt > > Complete log: https://pastebin.com/uCfqY4D8 > > Entire kernel config: https://pastebin.com/MRWGr3nv > > Root Cause Analysis: > The kernel warning is triggered in ipmr_free_table() at > net/ipv4/ipmr.c:440, where the multicast routing table (mr_table) is > being freed during network namespace exit (ipmr_rules_exit). > The warning indicates that the multicast forwarding cache count > (mfc_cache_cnt) is non-zero, implying that resources were not > correctly cleaned up prior to netns teardown. > This suggests a possible bug in reference counting or teardown logic > of the IPv4 multicast routing infrastructure. > Additionally, the environment is running with fail_usercopy fault > injection enabled, which deliberately triggers copy-from-user failures > to test kernel error paths. > While these failures are expected, they may interact with multicast > socket setup/teardown paths, exacerbating latent issues. I think this was fixed by commit c46286fdd6aa1d0e33c245bcffe9ff2428a777bd Author: Paolo Abeni Date: Thu May 15 18:49:26 2025 +0200 mr: consolidate the ipmr_can_free_table() checks.